This invention relates to optical analysis systems and methods for analyzing multiphase fluids, for example, reservoir hydrocarbons flowing in a tubular, pipe, or well.
In the petroleum industry, as in many other industries, ability to monitor flow of certain fluids in conduits, tubulars, process pipes and the like, especially in real time, offers considerable value. Oil and gas well operators often need to measure water, oil, gas flow rates, or a combination of these, during production, transportation and processing, and at various locations, such as downhole, at the wellhead, in transport pipelines, etc. Often the fluid is a mixture of multiple phases (oil, gas, water, even solids) and typically consists of many constituents (C1 and higher hydrocarbons, water, asphaltenes, etc.). This information aids in improving well production, making decisions regarding processes to apply to a well, preventing flow problems, and generally determining the well's performance.
While some techniques enable measuring flow rates within two phase mixtures, difficulty arises in determining individual volumetric and mass fractions and flow rates in three phase mixtures. Separators can be used to separate out one or more phases from the flow stream, but they introduce additional equipment and costs and typically require significant space. Other costly and time consuming procedures entail manual sampling of the mixture to obtain information regarding the individual volumetric or mass fractions. On the other hand, flow metering devices can be complex and can restrict flow creating significant pressure loss, such as when venturi based measurements are required, and do not determine the presence or amounts of particular constituents of the fluid.
In many instances, multiphase flow meters utilize a method to measure a flow rate of the entire flow stream and another process to measure volume fractions of oil, water and gas. This measured information, when applied to flow models, enables estimation of each of the individual phase flow rates. However, flow models make assumptions regarding flow characteristics, and do not account for uniqueness of particular fluid flow. In other words, application of flow models with measured total flow and volume fractions does not permit direct measurement of phase velocities and flow rates and does not determine the presence or amount of flow constituents.
Optical spectroscopy is an analytical technique that derives information about the system being evaluated by the interaction of that system with light in the UV to IR range. The interaction changes the properties of the light, specifically the frequency (color), intensity, polarization, or direction (scattering or refraction). Optical spectroscopy is used to analyze samples in an oil field. Optical spectroscopy techniques are costly, slow and cumbersome to implement and frequently require an elevated level of expertise at the well site.
Determining hydrocarbon fluid quality while drilling can impact real-time decisions such as which zones to test among numerous zones in a complex field, and the number and type of samples to take. When fluid samples are acquired, they must be evaluated for contamination, because high levels of contamination can render them useless for future analysis). Petroleum quality information can also affect decisions regarding drilling, logging, production, work-overs, etc. These services require substantial cost and down time. Natural systems, including geological and petroleum systems, rarely are conducive to a classic spectral analysis without extensive sample preparation. Additionally, classical spectroscopy has limited use in determining physical properties and can be costly and cumbersome to implement.
A relatively new technology employs multivariate optical elements (MOE) to analyze fluid flow, such as in petroleum production and pipelines. An MOE is an optical computer that offers advantageous of ruggedness, low cost and accuracy, while also being unobtrusive, and thus is well suited for application to analysis in a petroleum producing field and for petroleum pipeline monitoring in a hostile environment, such as production at elevated underground temperatures and pressures or in remote and hostile settings. MOE computer devices have been used to analyze static fluid samples, with the associated delays of collection, transport and testing. Further, MOE computer devices have been disclosed as useful in analyzing static and moving fluid flows. However, a need exists for improved methods and apparatus to analyze multiphase fluid flow through a tubular to determine constituents and properties of the fluid.